Load cell



A. E. SEED LOAD CELL Nov. 12, 1963 2 Sheets-Sheet 1 Filed June 28, 1959INVENTOR. ANIESE E. SEED 9 ATTOENEYS United States Patent 3,110,175 LOADCELL Aniese E. Seed, Toledo, Ohio, assignor to Toledo dcale Corporation,Toledo, Ghio, a corporation of Qhio Filed .luly 28, 1959, Ser. No.830,897 6 Claims. (ill. 73-141) This invention relates generally to loadweighing devices and in particular to load cells of the type which areutilized in conjunction with various strain gage devices to determinethe magnitude of a load applied to a load cell.

Load cells are utilized in many different fields where load forces areto be measured or masses are to be weighed. Load cells in conjunctionwith strain gage devices find particular application in perman ntinstallations in which the load cells are so located that it isimpossible or very difficult to provide maintenance for the loadweighing devices. In most applications it is impossible to center a loaddirectly over one load cell so that a plurality of the load cells mustbe used to support and measure a particular load. An outstanding exampleof this is a load weighing device for trucks. If it is impossible tocenter the load over one load cell then the off-center loading or torqueloading of a load cell and how it reacts thereto is very important.

In still other applications load cells are used to measure loads whichtransmit rotational torque to the load cell. For example, the screwdownscrew of a rolling mill applies a rotational torque to the measuringload cell, creating torque strains within the cell in the load sensitivearea.

The physical size of a load cell is important in that a standard line ofload cells of a particular geometry may perform well at one size whileanother size responds inefiiciently to an applied load.

Accordingly, it is an object of this invention to provide an improvedload cell which is efficient at all sizes, the cost of which is small,which effectively resists undesired rotational torque forces, and whichbalances off-center loading.

It is a further object of this invention to provide a load cell devicewhich may be formed from one piece of stock thereby providing lowmechanical hysteresis, has mounting surfaces for strain gage devices onwhich the stress is uniform and mounting surfaces from which bothpositive and negative stresses may be obtained.

In accordance with the above objects it is a feature of this inventionto provide a force measuring device comprising a pair of frames, each ofthe frames having a plurality of sides. Means are provided coupling oneside of one frame to one side of the other frame. Each of the coupledsides have mounting surfaces for load responsive devices such as straingages. If the frames are interlinked ihounting surfaces on the coupledsides are under compression when a compressive force is applied to theframes. If the frames are not interlinked mounting surfaces on thecoupled sides are under tension when a compressive force is applied tothe frames. The coupling means is advantageously a filleted couplingmember which is operable to make the mounting surfaces on the coupledsides more sensitive to stress and thus producing more measurabletension and compression for strain gages mounted thereon. The forcemeasuring device may be an integral device formed from one piece ofstock thereby reducing undesirable mechanical hysteresis effects.

It isdesirablc for each of the frames to have two parallel sides. If twoof the sides of each frame are parallel the number of mounting surfacesfor strain gage devices is doubled. Further, the mounting surfaces onthe parallel sides which are not coupled provide the opposite sign ofstress, i.e., positive or negative, to the sign of the Patented Nov. 12,1 $63 stress produced on the mounting surfaces on the coupled parallelsides. The load forces are then applied to the frames on theirnon-coupled parallel sides.

In the preferred embodiment shown in the drawings of this invention theframes are rectangular wherein the coupled parallel sides are equal inlength and coupled together at the center of their respective lengths.The load receiving sides, of course, are also equal in length and havemeans for receiving the load force at the center of their respectivelengths. it is to be noted that there are a number of geometricalconfigurations of frames which may be utilized which will embody theteachings of this invention, e.g., triangles, trapezoids, otherpolygons, advantageously regular polygons, etc. If mounting surfaces areprovided on rectangular frames on noncoupled parallel sides, then themeans for receiving a load on said non-coupled parallel sides preferablyincludes a filleted load receiving member at the load points to make themounting surface on the non-coupled parallel sides more sensitive .tostresses.

Other objects and advantages will become apparent to those skilled inthe art from the following description when taken into conjunction withthe accompanying drawings, in which:

FIG. I is a view in perspective of a load cell embodying the teachingsof this invention;

FIG. If is a plan view of FIG. 1;

FIG. III is a front view of FIG ll; and

FIG. IV is a side view of FIG Ill.

Referring to the figures there is shown a load cell comprising a pair ofrectangular frames designated generally at 29 and 3% Each of therectangular frames 20 and 39 has longer parallel sides 21, 22 and 31,32, respectively. One side 22 of the rectangular frame 20 is coupled ina non-parallel relationship to one side 31 of the rectangular frame 3%by a coupling member 49. It is to be noted that certain configurationswithin the scope and teachings of this invention need not be coupled ina nonparallel relationship to provide similar mounting surfaces.However, when sides of the frames are coupled in parallel relationship,a coupling member or fillet struc ture 4d, of necessity, must be placedbetween the sides to provide bending or stressed areas in the coupledsides when load forces are applied to the frames. The noncouplcd sides21 and 32 of the rectangular frames 20 and 30, respectively, areattached to load receiving means 50 and 69 through filleted loadreceiving coupling members 41 and 42. The load cell shown in thedrawings wherein each frame has two parallel sides therefore affordsfour mounting surfaces 23, 24 and 33, 34' upon which strain gage ordeflection sensitive devices 71 through 74 may be mounted.

When compressive load forces are applied to load receiving means 5t? andas the mounting surfaces 34 and 23 will be under tensile stress whilethe mounting surfaces 24- and 33 will be under compressive stress.

Advantageously, for use with tensile loads, apertures 51 and 61 areformed in the load receiving means 50 and 68, respectively. As can bestbe seen in FIG. IV the aperture 51 has been countersunk at 52 and 53. Asbest seen in FIG. III the aperture 61 has been countersunk at 62 and 63.After countersirfldng only a small portion of the cylindrical apertures51 and 61 remains centrally located in the load receiving means 50 and6%, respectively. When a load is connected to the load receiving meansthe contact with the cylindrical portion of the holes 51 and 61 isoperative to center the load forces on an axis formed by a line passingthrough the centers of the fillets it), 41 and 42, thereby preventingoff-center loading.

In the embodiment shown in the drawings the rectangular frames areinterlinked thus enabling the two rectangular frames Zil and Ell to beformed from a single piece through as shown in the drawings.

of stock which is shorter in length than a piece of stock required foran alternate embodiment which will now be described. Because of thesimplicity of design of the load cell the alternate modification,wherein the frames are not interlinked, is deemed not to be complicatedenough to require additional drawings. The frames Zil and 36 plus theload receiving means 56 and 69 can just as easily be formed into anintegral load cell from a single piece of stock when the planes 2% and39 are not interlinked. That is, what is now shown as mounting surfaces33 and 24 would be joined by the filleted coupling member as. The planesof the sides 37. and 22 opposite the mounting surfaces 33 and 24 of theframes 2% and 39 which are now coupled by the filleted coupling member 4would then provide mounting surfaces for strain gages or defiectiveresponsive devices. However, this modification wherein the frames arenot interlinked would not provide both positive and negative stresseswhen receiving either a compressive or a tensile load force at the loadreceiving members Ell and 6%. When the load force applied to the loadreceiving members 5 and so is compressive each of the four mountingsurfaces in the alternate modification of non-interlinked frames wouldhave tensile stresses thereon. Of course, when tensile forces areapplied to the above means 5%} and oi the mounting surfaces on thenon-interlinked modification would pro vide only compressive stress forthe strain gages to measure. Therefore, the preferred embodiment ofrectangularly interlinked frames is the configuration shown in thedrawing.

A second modification of the load cell shown in the drawing wouldprovide mounting surfaces that would have both positive and negativestresses. There is needed but one further step past the first alternateembodiment discussed in the preceding paragraph. That is, the frames 24and 33 would have their coupled sides 22 and 31 not interlinked.However, the load receiving means 5t} and 6i) would be sufficientlyenlarged so that they could be rotated ninety degrees and interlinkedwith the frames 2% and 33, respectively. If the load receiving means 5%and 69 were to be interlinked with the frames 2t) and 35 they would bepreferably shaped as rectangular frames rather than the rectangularblocks with round apertures therelf the load receiving means 59 and 6%were interlinked with the rectangular frames 2%) and 39, respectively,then the planes of the sides 21 and 32 where the filleted couplingmembers 41 and 42 are presently located would provide mounting surfacesfor strain gages that would be under compression when the load receivingmeans 5i and 6% were under compression. If, as previously assumed above,the frames 2% and 34} were not interlinked the planes of the sides 22and 31 which are presently coupled would then be free to providemounting surfaces which are under tension when a compressive load wasapplied to the load receiving means 59 and 60. Thus, the secondmodification would provide positive and negative stresses for use in ameasuring circuit.

As can most clearly be seen in FIGS. HI and IV, the machining or formingof the load cell of this invention from a single piece of stock is arelatively simple process since all of the fillets formed, whether theyare coupling fillet members or fillets formed in the sides of therectangular frames may be formed by parallel passes of a milling orother suitable machine. Therefore, the cost of the load cell is small.

Thus there is provided a force measuring device or a load cell whichcomprises a pair of interlinked frames, as shown in the drawings, havingtheir loading and linked points centered on the longer opposite sidesand in alignment for each frame. A mounting surface for a strain gage orother deflection responsive device is provided on the longer side ofeach frame opposite the point of loading to provide compression on thestrain gage when the unit is in tension and tension on the gage when theunit is in 4 compression. Such frame also has a gage mounting surface onthe interlinked sides opposite the link point to provide tension on thegage when the unit is in tension and compression when it is incompression.

The load cell of this invention may be utilized with bonded straingages. Since the load cell is constructed from a single piece of stockit has little mechanical hysteresis. "i" he load cell has linear springcharacteristics, may be made in a small physical size, has a littleresponse to torque loading, provides mounting surfaces for strain gageshaving the maximum stress in the unit, provides uniform stress across amounting surface of adequate area, and provides equal numbers ofmounting areas both compressive and tensile stresses.

In conclusion it is pointed out that while the illustrated exampleconstitutes a practical embodiment of my invention, I do not limitmyself to the exact details shown, since modification of the same may bemade without departing from the spirit of this invention.

Having described the invention, 1 claim:

1. A force measuring device comprising first and second frames; each ofsaid frames having a side that flexes wit .1 the frame is stressed, theremainder of the frame being suhciently rigid to apply the forcenecessary to flex said side; rigid mechanical means coupling a firstsurface of said side of said first frame to a first surface of said sideof said second frame, the coupling of said surfaces being limited to arelatively small area of each surface, and said coupled surfaces beingdisposed in spaced apart parallel planes; mounting surfaces for loadresponsive devices on a second surface of each of said coupled sidesopposite to the area of coupling; and means for applying a load to saidframes in a direction substantially perpendicular to said parallelplanes of said coupled surfaces and in alignment with the coupled areasof said surfaces, flexing said mounting surfaces.

2. A force measuring evice comprising first and second frames; each ofsaid frames having two parallel sides each of which flexes when theframe is stressed, the remainder of the frame being sufficiently rigidto apply the force necessary to flex said sides; rigid mechanical meanscoupling a first surface of one of said parallel sides of s id first itme to a first surface of one of said parallel 0.. es of said secondframe, the coupling of said surfaces being ited to a relatively smallarea of each surface, and said coupled surfaces being disposed in spacedapart parallel planes; mounting surfaces for load responsive devices ona second surface of each of said coupled sides opposite to the area ofcoupling; mounting surfaces for load responsive devices on a firstsurface of each of said non-coupled parallel sides; and means forapplying a load to said non-coupled parallel sides in a directionsubstantially perpendicular to said parallel planes of said coupledsurfaces and in alignment with the coupled areas of said surfaces,flexing said mounting surfaces.

3. A force measuring device comprising first and second frames; each ofsaid frames having two parallel sides each of which flexes when theframe is stressed, the remainder of the frame being sufllciently rigidto apply the force necessary to flex said sides; rigid mechanical meanscoupling a first surface of one of said parallel sides of said firstframe to a first surface of one of said parallel sides of said secondframe, the coupling of said surfaces being limited to a relatively smallarea of each surface, and said coupled surfaces being disposed in spacedapart parallel planes; mounting surfaces for load responsive devices ona second surface of each of said coupled sides opposite to the area ofcoupling; mounting surfaces for load responsive devices on a firstsurface of each of said non-coupled parallel sides; and means for appling a load to said non-coupled parallel sides in a directionsubstantially perpendicular to said parallel planes of said coupledsurfaces and in alignment with the coupled areas of said surfaces,flexing said mounting surfaces; said coupled sides being equal in lengthand coupled together at the center of their respective lengths.

4. A force measuring device comprising first and second frames; each ofsaid frames having two parallel sides each of which flexes when theframe is stressed, the remainder of the frame being sufiiciently rigidto apply the force necessary to flex said sides; rigid mechanical meanscoupling a first surface of one of said parallel sides of said firstframe to a first surface of one of said parallel sides of said secondframe, the coupling of said surfaces being limited to a relatively smallarea of each surface, and said coupled sunfaces being disposed in spacedapart parallel planes; mounting surfaces for load responsive devices ona second surface of each of said coupled sides opposite to the area ofcoupling; mounting surfaces for load responsive devices on a firstsurface of each of said non-coupled parallel sides; and means forapplying a load to said non-coupled parallel sides in a directionsubstantially perpendicular to said parallel planes of said coupledsurfaces and in alignment with the coupled areas of said surfaces,flexing said mounting surfaces; said non-coupled parallel sides beingequal in length and having said load applied at the center of theirrespective lengths.

5. A force measuring device comprising a pair of interlinked frames,each frame having a side that flexes when the frame is stressed, theremainder of the frame being sufficiently rigid to apply the forcenecessary to flex said side; rigid mechanical means coupling said sideof each frame in a spaced relationship; mounting surfaces for straingage devices on surfaces of said coupled sides opposite the area ofcoupling; and means for applying a load to said frames at points on saidframes opposite the coupling area on each of said frames to flex saidmounting surfaces on said coupled sides.

6. A force measuring device comprising a pair of interlinked frames,each frame having two sides that flex When the frame is stressed, theremainder of the frame being sufficiently rigid to apply the forcenecessary to flex said sides; rigid mechanical means coupling one ofsaid sides of each frame in a spaced relationship; mounting surfaces forstrain gage devices on surfaces of said coupled sides opposite the areaof coupling; each frame having its second flexible side opposite itscoupled side, which second side has a first surface adapted to receive aload and a second surface opposite said first surface to receive straingage devices; and means for applying a load to said first surfaces ofsaid second sides of said frames to flex the mounting surfaces for thestrain gage devices.

References Cited in the file of this patent UNITED STATES PATENTS2,421,222 Schaevitz May 27, 1947 2,520,923 Franzel et al. Sept. 5, 19502,576,417 Ruge Nov. 27, 1951 2,582,836 vRuge Jan. 15, 1952 2,680,376Shaw et a1. June 8, 1954 2,924,970 Samsel et al. Feb. 16, 1960

1. A FORCE MEASURING DEVICE COMPRISING FIRST AND SECOND FRAMES; EACH OFSAID FRAMES HAVING A SIDE THAT FLEXES WHEN THE FRAME IS STRESSED, THEREMAINDER OF THE FRAME BEING SUFFICIENTLY RIGID TO APPLY THE FORCENECESSARY TO FLEX SAID SIDE; RIGID MECHANICAL MEANS COUPLING A FIRSTSURFACE OF SAID SIDE OF SAID FIRST FRAME TO A FIRST SURFACE OF SAID SIDEOF SAID SECOND FRAME, THE COUPLING OF SAID SURFACES BEING LIMITED TO ARELATIVELY SMALL AREA OF EACH SURFACE, AND SAID COUPLED SURFACES BEINGDISPOSED IN SPACED APART PARALLEL PLANES; MOUNTING SURFACES FOR LOADRESPONSIVE DEVICES ON A SECOND SURFACE OF EACH OF SAID COUPLED SIDESOPPOSITE TO THE AREA OF COUPLING; AND MEANS FOR APPLYING A LOAD TO SAIDFRAMES IN A DIRECTION SUBSTANTIALLY PERPENDICULAR TO SAID PARALLELPLANES OF SAID COUPLED SURFACES AND IN ALIGNMENT WITH THE COUPLED AREASOF SAID SURFACES, FLEXING SAID MOUNTING SURFACES.